aalborg universitet smart-spider autonomous self-driven in ... · where the conventional...

Aalborg Universitet

Smart-Spider

Autonomous self-driven in-line robot for versatile pipeline inspection

Qu, Ying; Durdevic, Petar; Yang, Zhenyu

Published in:IFAC-PapersOnLine

DOI (link to publication from Publisher):10.1016/j.ifacol.2018.06.385

Publication date:2018

Document VersionPublisher's PDF, also known as Version of record

Link to publication from Aalborg University

Citation for published version (APA):Qu, Y., Durdevic, P., & Yang, Z. (2018). Smart-Spider: Autonomous self-driven in-line robot for versatile pipelineinspection. IFAC-PapersOnLine, 51(8), 251-256. https://doi.org/10.1016/j.ifacol.2018.06.385

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https://doi.org/10.1016/j.ifacol.2018.06.385

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https://doi.org/10.1016/j.ifacol.2018.06.385

IFAC PapersOnLine 51-8 (2018) 251–256

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2405-8963 © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.Peer review under responsibility of International Federation of Automatic Control.10.1016/j.ifacol.2018.06.385

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10.1016/j.ifacol.2018.06.385 2405-8963

Smart-Spider: Autonomous Self-drivenIn-line Robot for Versatile Pipeline

Inspection �

Ying Qu ∗ Petar Durdevic ∗ Zhenyu Yang ∗

∗ Department of Energy Technology, Aalborg University, EsbjergCampus, Niels Bohrs Vej 8, 6700 Esbjerg, Denmark (e-mail:

[email protected], [email protected], [email protected]).

Abstract: This paper presents the design and development of a conceptual prototype of anautonomous self-driven inline inspection robot, called Smart-Spider. The primary objective is touse this type of robot for offshore oil and gas pipeline inspection, especially for those pipelineswhere the conventional intelligent pigging systems could not or be difficult to be deployed. TheSmart-Spider, which is real-time controlled by its own on-board MCU core and power suppliedby a hugged-up battery, is expected to execute pipeline inspection in an autonomous manner.A flexible mechanism structure is applied to realize the spider’s flexibility to adapt to differentdiameters of pipelines as well as to handle some irregular situations, such as to pass throughan obstacled areas or to maneuver at a corner or junction. This adaption is automaticallycontrolled by the MCU controller based on pressure sensors’ feedback. The equipped devices,such as the selected motors and battery package, as well as the human-and-machine interfaceare also discussed in detail. Some preliminary laboratory testing results illustrated the feasibilityand cost-effective of this design and development in a very promising manner.

Keywords: Pipeline inspection, inline robot, autonomous control, flexible legs, HMI interface.

1. INTRODUCTION

Pipelines, used for offshore gas, oil and water transporta-tion, tend to be corroded after some time. Many pipelinesare located in some harsh marine environment, such as onor under the seabed, or even deep underground, and the ge-ometries and configurations of the pipeline systems can bevery complicated. The condition inspection and integritycheck of these pipelines can be very challenging, and evenimpossible by deploying the conventional inspection tools,such as the intelligent pig systems, even though often theeconomic cost can also be tremendous, see Christian (2016)and Iszmir (2012).

Many existing commercial inline robots need to beequipped with tethers/cables for data transmission andpower supply. Thereby, the inspection geometries is quitelimited by these tethers/cables. See Young (2012). Acrawler-type pipeline inspection robot is designed to in-spect 80-100 mm diameter indoor pipelines in that paper.The four-bar mechanisms is introduced to assure that theflexible diameter of the robot can expand to firmly gripthe pipeline inner surface. However, this robot still needscables for transmitting the commands and the inspectiondata between the remote workstation and the robot.

An autonomous mobile robot for pipeline exploration,called FAMPER, is described in Jong (2010). Four inde-pendent suspensions are applied to link each caterpillar

� The authors would like to the support from Danish HydrocarbonResearch and Technology Centre(DHRTC) through DHRTC RadicalProject Programme

track and the central body, which structure makes thecaterpillar track parts can contract in a small scale toadapt to bended pipelines. Because of the independentspeed control of the four caterpillars, it has efficient steer-ing capability to go through the pipelines with differ-ent branches. However, this robot can only be used forpipelines with a fixed diameter, that is 150 mm.

MRINSPECT V, a fixed diameter inline robot for 8-inchinner diameter pipelines is developed and presented in Se(2008). This inline robot can realize part of autonomousnavigation, and the power for the electronic system andthe motors is supported by the on board batteries. Be-sides that, a differential driving structure is adopted onthe mechanism design, which makes the motion of theproposed robot adapt to different pipeline shapes. More-over, the application of clutches is also highlight, whichis able to select the suitable driving method based ondifferent conditions for saving energy. The mobility and theefficiency performance of the robot are validated throughexperiments. However, although some wheels are installedon the two battery packages, there are no actuators onthem. Thus, the motion of the two battery carriages cannotbe controlled directly by the controller, but only depend onthe push and pull from the other two actuator carriages.Furthermore, the proposed robot lacks the flexibility ofadapting to different pipeline diameters.

An innovative Pipeline Inspection Gauge (PIG) for in-dustrial pipelines with small diameters is designed anddeveloped in Firas (2015), the functions of which are toclean and inspect pipelines. The diameter of the proposed

Proceedings of the 3rd IFAC Workshop onAutomatic Control in Offshore Oil and Gas ProductionMay 30 - June 1, 2018. Esbjerg, Denmark

Copyright © 2018 IFAC 251


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252 Ying Qu et al. / IFAC PapersOnLine 51-8 (2018) 251–256

PIG can adjusted to adapt pipelines with 6” to 14” innerdiameters, by adapting its shirts. Ultra Sonic sensors andArduino software are applied to inspect the diameter ofthe pipeline. Several arms are configured on the proposedrobot to maintain the moving speed and the position asexpected. The feasibility of the inline motion is validatedusing the Solidworks motion simulation tools. However,this robot model is only at the simulation stage, therefore,no physical model or experiments has been reported.

Without concerning to use any tethers or cables, a con-ceptual prototype inline robot, called Smart-Spider, isdesigned and developed in this work. A flexible mechanicalstructure is designed in order to handle versatile pipediameters, and the control cores and electronic system aswell as a Graphical User Interface (GUI) are also designedaccordingly.

In this paper, the flexible mechanism structure is describedin detail in Section 2. Section 3 describes the automaticcontrol mechanism implemented in the MCU to real-timeadjust the legs to different conditions based on the pres-sure variation on the wheels. The implementation of theproposed pipeline inspection robot platform, including thecontroller, some devices’ specifications and the preliminaryexperimental results, are described in Section 4 and theconclusion are followed in Section 5.

2. ARCHITECTURE OF THE SMART-SPIDER

2.1 Whole Smart-Spider System

The Smart-Spider system, as shown in Fig. 1, is composedof the robot device and the workstation. The Smar-Spidercan move inline for performing some tasks automatically,without any tethers or cables connecting to the worksta-tion. Regarding to the spider itself, the mechanism struc-ture consists two parts: the main body and the flexiblemechanism. The electronic system manages motion con-trol, leg automatic adaption, data collection and storageetc. On the remote workstation side, the graphical user in-terface (GUI) are used for mainly two purposes: (1)sendingstart and end commands at the beginning and the endof one automatic inspection experiment; (2)monitoringthe (pseudo-) real-time information in the experimentalstage, via wireless communication between the robot andworkstation.

Fig. 1. The whole system of the inline inspection robot -the Smart-Spider

The main mechanism structure is represented in Fig. 2,which is composed of two parts: the tube body and thethree flexible clutch mechanisms. Both of these two partsare processed by aluminium alloy. Inside the tube body isthe rack for the electronic system and the three flexibleclutch sets. The electronic system, consisting of a batteryand two layers of electronic PCBs and components, isfixed on the tube inside. On the exterior surface of thetube body, the three sets of flexible clutch mechanismsare integrated with 120 degrees interval angle, which canmake the Smart-Spider suit well for pipelines with roundcross section. Besides, two transparent acrylic domes areassembled at the front and the rear sides of the tube bodyrespectively.

Fig. 2. The mechanism structure of the Smart-Spider

The length of the Smart-Spider is 426 mm and the exteriordiameter is 300 mm. Based on the flexible mechanism,the exterior diameter of the Smart-Spider can adjustfrom 450 mm to 575mm, which means the variation ofthe flexible mechanisms can reach 78%. The diametertransmission range of the Smart-Spider is represented inFig. 3. Therefore, the Smart-Spider can be applied for theinspection tasks in the pipelines with the diameter in thisrange.

Fig. 3. The diameter transmission range of the Smart-Spider can be from 450 mm to 575 mm

2.2 Flexible mechanism

Three sets of flexible wheel mechanisms are integrated inthe Smart-Spider, and all their structures are completelysame. Each of these flexible wheel mechanisms consistsof three units: the driving mechanism, the linkage clutchmechanism and the wheel units, shown as in Fig. 4 andFig. 5, respectively. In order to be more compact and moreflexible, a screw rod is applied to replace the traditionalspring axe, which was used in Young (2010) and Young(2012), and an improved 4-bar structure is designed forthe linkage clutch mechanism, compared with the designin Fa (2015). Every wheel unit is composed of two setsof wheels and every wheel set consists two wheels. Each

IFAC OOGP 2018Esbjerg, Denmark. May 30 - June 1, 2018

252

wheel set is driven by a DC motor, which is equipped witha worm gear box, as shown in Fig. 5.

The driving mechanism is responsible for actuating the4-bar linkage clutch mechanisms to extend or contract,followed the wheel units to adjust to different pipelinediameters. The screw rod is driven by a stepper motor torevolve clockwise or anticlockwise. Therefore, the U-shapeslider and the connector slider crossing on the screw rodcan move forward and backward respectively. Then, theangle in the 4-bar linkage clutch transforms according tothe position of the sliders, which determines the exteriordiameter of the Smart-Spider.

Wheels

4-bar linkageclutch mechanism

Stepper motorPressure Sensor

Connector slider

U-shapeslider

Screw rod

Driving mechanism

Wheel unit

θ

Fig. 4. The horizontal view of the flexible mechanism ofthe Smart-Spider

Fig. 5. The top view of the flexible mechanism of theSmart-Spider

The force relationship between the force on the wheelsand the pressure on the sliders is shown as in Fig. 6.Through this relationship and the pressures measuredby the pressure sensors, the pressures and the frictionforces between the wheels and the pipeline inner surfacecan be calculated. The friction forces are caused by thepressures, and suitable friction forces ensure the Smart-Spider moving smoothly. Therefore, these pressures andfriction forces are critical to the dynamics of the robot.

The length of the bar PE is l. The length of ME and theslider bar SE can be considered to be the same, which isrepresented as l′. The torque on point P relative to pointE, which is TP , and the torque on point M relative to PointE, which is TM , are equal, described in equation (1).

TP = TF (1)

The torque on point P relative to point E can be calculatedas:

TP = FP · cos θ · l + Ff · sin θ · l= FP · l · (cos θ + µ · sin θ) (2)

where FP is the pressure on the P point, Ff is the frictionbetween the wheels and the pipeline inner surface and µis the friction coefficient.

The torque on point S relating to point E is:

TF = F1 · l′ (3)

Therefore, F1 can figure out. Then through dividing F1,the force on the slider bar F2 is:

F2 = F1 · cos(α− 90◦) (4)

Because α = 180◦ − 2θ, F2 can be represented as:

F2 = F1 · cos(180◦ − 2θ − 90◦) = F1 · sin(2θ) (5)

The pressure on the slider FS , which is collected by thepressure sensor, can be got by dividing F2:

FS = F2 · cos θ (6)

θ θ

'l

l

'l

Fs

2F

1F

FP

P

M

SE

Ff

Fig. 6. The force analysis of the linkage clutch mechanism

3. IMPLEMENTATION

3.1 Flexible mechanism motion control strategy

The motion of the flexible mechanisms are controlled bythe MCU based on the pressure data between the wheelsand the pipeline inner surface, which are related to thepressures between the connector slider and the U-shapeslider. In normal straight pipeline without diameter trans-formation, the pressures are within the threshold ranges.For some special pipelines, such as oil pipelines, the frictionbetween the wheels and the pipeline inner surface, which isdecided by the pressure between them, must be big enoughto guarantee the Smart-Spider’s normal rolling movement.However, when the inner diameter of the pipeline changes,the pressures on the wheels will change, and the pressuresbetween the sliders will transform accordingly. The flexiblemechanisms will contract when the pressures exceed thethreshold ranges when the pipeline inner diameter changesinto smaller, for example, there is an obstacle or a corner.On the contrary, the flexible mechanisms will extend whenthe pressures reduce lower than the threshold ranges.

The pressure threshold range for different flexible mecha-nisms on different positions can be different, that is, thepressure threshold for the two bottom flexible mechanismsare much higher than the top one if the robot moves mainlyin the horizontal way. In some situations, the attitudeof the Smart-Spider changes during moving along thepipeline, and if the variation of the attitude is big enough,a rolling motion can happen. Therefore, the positions ofthe previous top and bottom flexible mechanisms may ex-change. In the MCU, the pressure threshold ranges for eachflexible mechanisms need to adjust according to specificattitude orientations, where the attitude is collected by


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Ying Qu et al. / IFAC PapersOnLine 51-8 (2018) 251–256 253

wheel set is driven by a DC motor, which is equipped witha worm gear box, as shown in Fig. 5.

The driving mechanism is responsible for actuating the4-bar linkage clutch mechanisms to extend or contract,followed the wheel units to adjust to different pipelinediameters. The screw rod is driven by a stepper motor torevolve clockwise or anticlockwise. Therefore, the U-shapeslider and the connector slider crossing on the screw rodcan move forward and backward respectively. Then, theangle in the 4-bar linkage clutch transforms according tothe position of the sliders, which determines the exteriordiameter of the Smart-Spider.

Wheels

4-bar linkageclutch mechanism

Stepper motorPressure Sensor

Connector slider

U-shapeslider

Screw rod

Driving mechanism

Wheel unit

θ

Fig. 4. The horizontal view of the flexible mechanism ofthe Smart-Spider

Fig. 5. The top view of the flexible mechanism of theSmart-Spider

The force relationship between the force on the wheelsand the pressure on the sliders is shown as in Fig. 6.Through this relationship and the pressures measuredby the pressure sensors, the pressures and the frictionforces between the wheels and the pipeline inner surfacecan be calculated. The friction forces are caused by thepressures, and suitable friction forces ensure the Smart-Spider moving smoothly. Therefore, these pressures andfriction forces are critical to the dynamics of the robot.

The length of the bar PE is l. The length of ME and theslider bar SE can be considered to be the same, which isrepresented as l′. The torque on point P relative to pointE, which is TP , and the torque on point M relative to PointE, which is TM , are equal, described in equation (1).

TP = TF (1)

The torque on point P relative to point E can be calculatedas:

TP = FP · cos θ · l + Ff · sin θ · l= FP · l · (cos θ + µ · sin θ) (2)

where FP is the pressure on the P point, Ff is the frictionbetween the wheels and the pipeline inner surface and µis the friction coefficient.

The torque on point S relating to point E is:

TF = F1 · l′ (3)

Therefore, F1 can figure out. Then through dividing F1,the force on the slider bar F2 is:

F2 = F1 · cos(α− 90◦) (4)

Because α = 180◦ − 2θ, F2 can be represented as:

F2 = F1 · cos(180◦ − 2θ − 90◦) = F1 · sin(2θ) (5)

The pressure on the slider FS , which is collected by thepressure sensor, can be got by dividing F2:

FS = F2 · cos θ (6)

θ θ

'l

l

'l

Fs

2F

1F

FP

P

M

SE

Ff

Fig. 6. The force analysis of the linkage clutch mechanism

3. IMPLEMENTATION

3.1 Flexible mechanism motion control strategy

The motion of the flexible mechanisms are controlled bythe MCU based on the pressure data between the wheelsand the pipeline inner surface, which are related to thepressures between the connector slider and the U-shapeslider. In normal straight pipeline without diameter trans-formation, the pressures are within the threshold ranges.For some special pipelines, such as oil pipelines, the frictionbetween the wheels and the pipeline inner surface, which isdecided by the pressure between them, must be big enoughto guarantee the Smart-Spider’s normal rolling movement.However, when the inner diameter of the pipeline changes,the pressures on the wheels will change, and the pressuresbetween the sliders will transform accordingly. The flexiblemechanisms will contract when the pressures exceed thethreshold ranges when the pipeline inner diameter changesinto smaller, for example, there is an obstacle or a corner.On the contrary, the flexible mechanisms will extend whenthe pressures reduce lower than the threshold ranges.

The pressure threshold range for different flexible mecha-nisms on different positions can be different, that is, thepressure threshold for the two bottom flexible mechanismsare much higher than the top one if the robot moves mainlyin the horizontal way. In some situations, the attitudeof the Smart-Spider changes during moving along thepipeline, and if the variation of the attitude is big enough,a rolling motion can happen. Therefore, the positions ofthe previous top and bottom flexible mechanisms may ex-change. In the MCU, the pressure threshold ranges for eachflexible mechanisms need to adjust according to specificattitude orientations, where the attitude is collected by


253


Beginning

Collecting attitude data

Attitude data from sensors

Pressure data are in threshold range

N

Traditional control algorithm unit

PWM & direction control signals

Y

Driver PCBs

Stepper motors

Being stable out of threshold

Y

N

Judging the flexible mechanisms’position

Pressure data from sensors

Collecting pressure data

Fig. 7. The flow chart of the flexible mechanism motioncontrol based on pressure data

the attitude sensor and the threshold ranges are set by adhoc experimental experience at this moment.

The motion strategy of the flexible mechanisms in theMCU is shown in Fig. 7, and this is for one control-cycleperiod. At first, the positions of the three flexible mecha-nisms are estimated based on the proposed robot’s attitudemeasurement, and the threshold ranges for each one canbe decided, where the attitude data are collected by theattitude sensor. Based on the definite threshold ranges, thepressure data for each flexible mechanism are comparedwith the range. For calculation efficiency, these ranges aredirectly defined for the pressure between the sliders, whichomits calculating the pressure on the wheels. If one or morepressures exceed higher or lower than the threshold ranges,the MCU will not drive the motors to transform the Smart-Spider’s diameter immediately, but will store the pressuresituations until several sampling periods later. If all thesepressures are beyond the threshold ranges, the MCU willcontrol the stepper motors by sending PWM signals to thedriver boards after the PI controller. All the three flexiblemechanisms contracting or extending at the same time canensure the equilateral triangle mechanical structure of thethree flexible mechanisms, which is a stable structure forthe Smart-Spider to fit motion requirements, see Se (2008).

3.2 Task processing

The tasks of the electronic system can be divided into twocategories: real-time tasks and non-realtime tasks, shownas in Fig. 8. The real-time tasks are implemented by aMCU PCB, which is equipped with STM32F407 controlcore. And the non-realtime tasks are implemented by aRaspberry Pi, installed with Debian operational system.Data and commands are transmitted between the MCUand the Raspberry Pi through UART.

In the real-time control system, the collection and theanalysis of all the sensor data, and the motion control ofall the stepper motors and DC motors are handled by theMCU. The pressure data from the three pressure sensorsand the attitude information from the attitude sensor arecollected by the MCU. Moreover, the flexible mechanisms’motions based on the pressure and each DC motor’s speedis judged in the control strategy in the MCU. Then, thePWM signals for controlling the stepper motors and theDCmotors are generated by the MCU to the driver boards.Meanwhile, the real time sensor data are transmitted tothe Raspberry Pi for displaying on the GUI.

Regarding to the non-realtime control system, the work-station communicates with the Raspberry Pi through Wifiin experimental environment. The GUI system is designedto monitor the image collected by the on-board camera,and display the (pseudo-) real-time data of the Smart-Spider. Besides, users can configure the inline robot’smotion mode (Auto or Manual) and the motors’ motionsituations through the GUI, which are transmitted to theMCU. Meanwhile, all the real-time data are written intoa SD card for storage and post analysis.

Fig. 8. The structure of the electronic system

3.3 Actuators and Battery

DC Motor DC motors with a worm gear box are usedto output a given torque on the purpose of driving thewheels to move in a given direction at a specific speed.Every two DC motors are fixed on the top of one flexiblemechanism, so there are six DC motors in total in theSmart-Spider. Each DC motor is equipped with a wormgear box to increase the output torque, so each DC motorwith a gear box can actuate two wheels. The speed andthe direction of the DC motors are controlled by the MCUcontroller, based on the requirement of the motion. Thespecifications of the DC motor with a worm gear box arelisted in Table. 1.

Stepper Motor The function of the stepper motor kits inthe Smart-Spider is to actuate the screw rod, so that theflexible mechanisms can stretch or contract. Three stepper


254

Table 1. Specifications of the DC Motors

Specification Value

Nominal Voltage 12.0 VNominal Speed 28 rpmMax. Speed 72 rpm

Rated Current 0.6 AMax. Current 2.3 ARated Torque 12.0 Kg.cmMax. Torque 57.0 Kg.cm

Reduction ratio 1:108

motors are used, and each stepper motor kit is equippedat the end of a screw rod, which follows the motion of themotors by a coupling connection. To get strong enoughtorque for driving the flexible mechanisms, a gear box isapplied in the stepper motor kit. The reduction ratior ofthe gear box is 1/52, and the static torque can reach 12.0Kg.cm. The specification details of the stepper motor witha gear box are listed in Table. 2.

Table 2. Specifications of the Stepper Motors

Specification Value

Step Angle 1.8 degreeNominal Voltage 10.0 VRated Current 1.0 AStatic Torque 12.0 Kg.cmReduction ratio 1:52

Battery The Li battery is the main source of the wholeelectronic system, the details of the specifications of whichis listed in Table. 3. The capacity can reach as high as 8400mAh, although the size is small enough to fixed inside thebody tube. Due to the rated current of the DC motors is0.6 A, and the rated current of the stepper motors is 1.0 A,the battery can support the Smart-Spider moving insidethe pipeline for around 2 hours.

Table 3. Specifications of the Battery

Specification Value

Type LiPoOutput 11.1 VCells 3S

Capacity 8400 mAhSize 155×44×45mm

4. EXPERIMENTS

In this experiment, the automatic motion of the Smart-Spider and the feasibility of the flexible mechanisms areverified in the laboratory pipeline, the material of whichis PVC and the inner diameter is 500 mm. The proposedinline robot moves forward automatically completely aftera simple launching.

Firstly, the Smart-Spider moves in a pipeline with smoothinner surface, that is, there is no obstacle inside of thepipeline. Before the experiments, the initial attitude of theSmart-Spider is that the two bottom flexible mechanismsare nearly at the horizontal flat, that is, the top flexiblemechanism is perpendicular to the horizontal flat. Sothe initial pitch(around -4deg) and the roll(around 1deg)of the inline robot is very small, shown as in Fig. 9.And the initial pressure forces on the flexible mechanismsare approximately 118 N, 88 N and 10 N respectively,

shown in Fig. 10. From the diagrams we can see that theSmart-Spider can move smoothly along the inner pipeline,although a small rolling happens, the attitude of the robotkeeps stable.

The four steps of the pipeline robot overcoming an obstaclein the pipeline are shown as in Fig. 13, and the pressuredata and the attitude information during the process areshown as in Fig. 11 and Fig. 12. From 0 s to around20 s, the Smart-Spider keeps moving forward smoothly,although some small frequent fluctuations are generatedbecause of the dumps of the pipeline. At around 20 s, therobot begins overcoming the obstacle. When the pressuresincrease and exceed higher than the threshold, and holdhigher for 10 sampling periods, the three flexible mecha-nisms start contracting at the same time, driven by theMCU until the pressures fall back to the threshold bandsagain. From around 42 s, the robot begins leaving theobstacle, so the pressures on the flexible mechanisms de-crease suddenly. Therefore, the flexible mechanisms startstretching to adjust to the pipeline diameter. During thisprocess, the variations of the attitude of the Smart-Spideris small, that are less than 1.5 deg for roll and around5 deg for pitch respectively. Therefore, the rolling of theSmart-Spider can be ignored during this process, so thethreshold range for each flexible mechanism does not needto be adjusted during the entire experiment.

0 20 40 60 80 100

Time(s)

0

20

40

60

80

100

120

140150

Pre

ssur

e(N

)

LeftRightTop

Fig. 9. The pressure on the three flexible mechanisms ofmoving in smooth situation

0 20 40 60 80 100

Time(s)

-5-4-3-2-1012345

Ang

le(d

eg)

PitchRoll

Fig. 10. The attitude of moving in smooth situation

The user interface of the Smart-Spider system is shown inFig. 14. Not only the real-time image from the camera,the graphical motion situations and some sensor data canbe monitored on this interface, but also some motioncommands can be handled by the buttons.

From the experiment results, the motion feasibility and theflexible mechanisms’ automatic control are validated, andthe expected functions of the Smart-Spider are realizedsatisfactorily.


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Ying Qu et al. / IFAC PapersOnLine 51-8 (2018) 251–256 255

Table 1. Specifications of the DC Motors

Specification Value

Nominal Voltage 12.0 VNominal Speed 28 rpmMax. Speed 72 rpm

Rated Current 0.6 AMax. Current 2.3 ARated Torque 12.0 Kg.cmMax. Torque 57.0 Kg.cm

Reduction ratio 1:108

motors are used, and each stepper motor kit is equippedat the end of a screw rod, which follows the motion of themotors by a coupling connection. To get strong enoughtorque for driving the flexible mechanisms, a gear box isapplied in the stepper motor kit. The reduction ratior ofthe gear box is 1/52, and the static torque can reach 12.0Kg.cm. The specification details of the stepper motor witha gear box are listed in Table. 2.

Table 2. Specifications of the Stepper Motors

Specification Value

Step Angle 1.8 degreeNominal Voltage 10.0 VRated Current 1.0 AStatic Torque 12.0 Kg.cmReduction ratio 1:52

Battery The Li battery is the main source of the wholeelectronic system, the details of the specifications of whichis listed in Table. 3. The capacity can reach as high as 8400mAh, although the size is small enough to fixed inside thebody tube. Due to the rated current of the DC motors is0.6 A, and the rated current of the stepper motors is 1.0 A,the battery can support the Smart-Spider moving insidethe pipeline for around 2 hours.

Table 3. Specifications of the Battery

Specification Value

Type LiPoOutput 11.1 VCells 3S

Capacity 8400 mAhSize 155×44×45mm

4. EXPERIMENTS

In this experiment, the automatic motion of the Smart-Spider and the feasibility of the flexible mechanisms areverified in the laboratory pipeline, the material of whichis PVC and the inner diameter is 500 mm. The proposedinline robot moves forward automatically completely aftera simple launching.

Firstly, the Smart-Spider moves in a pipeline with smoothinner surface, that is, there is no obstacle inside of thepipeline. Before the experiments, the initial attitude of theSmart-Spider is that the two bottom flexible mechanismsare nearly at the horizontal flat, that is, the top flexiblemechanism is perpendicular to the horizontal flat. Sothe initial pitch(around -4deg) and the roll(around 1deg)of the inline robot is very small, shown as in Fig. 9.And the initial pressure forces on the flexible mechanismsare approximately 118 N, 88 N and 10 N respectively,

shown in Fig. 10. From the diagrams we can see that theSmart-Spider can move smoothly along the inner pipeline,although a small rolling happens, the attitude of the robotkeeps stable.

The four steps of the pipeline robot overcoming an obstaclein the pipeline are shown as in Fig. 13, and the pressuredata and the attitude information during the process areshown as in Fig. 11 and Fig. 12. From 0 s to around20 s, the Smart-Spider keeps moving forward smoothly,although some small frequent fluctuations are generatedbecause of the dumps of the pipeline. At around 20 s, therobot begins overcoming the obstacle. When the pressuresincrease and exceed higher than the threshold, and holdhigher for 10 sampling periods, the three flexible mecha-nisms start contracting at the same time, driven by theMCU until the pressures fall back to the threshold bandsagain. From around 42 s, the robot begins leaving theobstacle, so the pressures on the flexible mechanisms de-crease suddenly. Therefore, the flexible mechanisms startstretching to adjust to the pipeline diameter. During thisprocess, the variations of the attitude of the Smart-Spideris small, that are less than 1.5 deg for roll and around5 deg for pitch respectively. Therefore, the rolling of theSmart-Spider can be ignored during this process, so thethreshold range for each flexible mechanism does not needto be adjusted during the entire experiment.

0 20 40 60 80 100

Time(s)

0

20

40

60

80

100

120

140150

Pre

ssur

e(N

)

LeftRightTop

Fig. 9. The pressure on the three flexible mechanisms ofmoving in smooth situation

0 20 40 60 80 100

Time(s)

-5-4-3-2-1012345

Ang

le(d

eg)

PitchRoll

Fig. 10. The attitude of moving in smooth situation

The user interface of the Smart-Spider system is shown inFig. 14. Not only the real-time image from the camera,the graphical motion situations and some sensor data canbe monitored on this interface, but also some motioncommands can be handled by the buttons.

From the experiment results, the motion feasibility and theflexible mechanisms’ automatic control are validated, andthe expected functions of the Smart-Spider are realizedsatisfactorily.


255


0 20 40 60 80 100

Time(s)

0

20

40

60

80

100

120

140150

Pre

ssur

e(N

)

LeftRightTop

Fig. 11. The pressure on the three flexible mechanisms ofovercoming an obstacle

0 20 40 60 80 100

Time(s)

-4

-3

-2

-1

0

1

2

3

4

Ang

le(d

eg)

PitchRoll

Fig. 12. The attitude of overcoming an obstacle

Fig. 13. The three-stage motions of the Smart-Spiderduring the experiment (a)moving smooth stage(b)preparing-to-overcome stage (c)on-obstacle stage(d)obstacle-overcome stage

Fig. 14. The user interface of the Smart-Spider

5. CONCLUSION

In this paper, an automatic inline inspection robot pro-totype, called Smart-Spider, is designed and developed.It can move along the pipeline to implement some tasksand handle some specific conditions, such as an obstacle,completely automatically, which dues to the applicationof the MCU controller and the flexible mechanisms. Be-sides, without the limitation of any tethers or cables, theproposed robot’s motion can be more flexible and moredistant, which are important features for the inspectionof some complex industrial pipelines. Lastly, the stabilityof the robot’s motion and the feasibility of the automaticcontrol of the flexible mechanisms are verified in the labo-ratory pipeline, and the experimental results are presentedand analyzed.

For the future Smart-Spider generations, many improve-ments will be applied:

(1) On-board algorithms for automatic path recognitionand planning for complex or unknown pipeline envi-ronments;

(2) Integration with inspection tools for specific applica-tions;

(3) Strategies for self-monitoring and self-rescue in caseof getting stuck inside the pipelines;

(4) Smart power management design from informationcollection and energy efficiency aspects.

ACKNOWLEDGEMENTS

The authors would like to thank the support from DHRTCRadical Project Programme, and particularly thanks goto DHRTC colleagues: Kristine W. Hilstrm and Lene H.Poulsen, AAU colleagues: Yunlong Wang, Simon Pedersenand H. Enevoldsen, for many valuable discussions andtechnical supports.

REFERENCES

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Young-Sik, K., Bae, L., In, W., Whee, K. and Byung,Y. (2011). A Flat Pipeline Inspection Robot withTwo Wheel Chains. IEEE International Conference onRobotics and Automation, 5141-5146.

Fa, C., Lih, H., Chih, L., Wei, W., Jeng, L., Shun, W.and Kai, C. (2015). Design of a pipeline inspectionrobot with belt driven ridged cone shaped skate model.2015 IEEE International Conference on Robotics andBiomimetics (ROBIO), 787-792.

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